DESCRIPTION (Applicant's Description) Breast cancer is associated with endogenous hormone levels but the exact relationships - and underlaying mechanisms remain unclear. Recent studies have suggested that women who have experienced preeclampsia during pregnancy, and women who were exposed to preeclampsia when they were themselves developing fetuses in utero might be at reduced risk for breast cancer. Because preeclampsia is characterized by abnormal levels of circulating hormones, these relationships may be due to hormonal effects on the developing fetus or to hormonal profiles that predispose women both to preeclampsia during pregnancy and to a reduced risk of breast cancer later in life. We propose to investigate the relationship between breast cancer and both personal history of preeclampsia during a prior pregnancy and exposure to preeclampsia in utero by conducting a large study using linked birth and cancer registry data from New York State. Because endometrial cancer is even more clearly linked to estrogens than is breast cancer, we will also examine the association between preeclampsia and risk for endometrial cancer using this same study design. Using a case-control design, we will analyze anonymous, linked birth record and tumor registry data from the New York State and New York City Health Departments as our primary information source. Cases will be identified through the New York State Cancer Registry, defined as women who were diagnosed with breast or endometrial cancer between 1978 and 1996. Each woman's cancer registry record will then be matched with those pertaining to all of her pregnancies in New York subsequent to 1961 (the earliest year of computerized birth records). Controls will be frequency matched to cases by year and hospital of their first pregnancy, or of their own birth. Preeclampsia during the first pregnancy will be the primary exposure of interest for subjects having a first pregnancy in New York after 1961. For subjects born in New York after 1961, maternal preeclampsia during that gestation (i.e., in utero exposure) will be the primary exposure of interest. Logistic regression analyses will be used to determine the independent effects of personal history of preeclampsia and in utero exposure to preeclampsia on cancer risk, and to assess the influence of potential confounding factors. This study is large enough to provide power to explore effect modification of the cancer-preeclampsia association by selected factors, including age at cancer diagnosis, age at first pregnancy, and race/ethnicity. Findings from this study can suggest specific avenues for future research among women who have been affected by preeclampsia to better understand the relationships between hormonal profiles in life and the etiology of breast and endometrial cancer.